Electrical heating element



PERCY A. E. ARMSTRONG, OF LO'UDONVILLE, NEW YORK.

'ELECTRICAL HEATING- ELEMENT.

Specification of Iietters Patent.

No Drawing. Application filed May 1, 1919, Serial No.293,927. RenewedOctober 1, 1921. Serial No. 504,676.

To all whom it may concern Be it known that I, PERCY A. E. ARM- STRONG,a subject of the King of Great Brit- .loyed with iron and carbon.

ain, and a resident of Loudonville, county of Albany, State of New York,have invented certain new and useful Improvements in Electrical HeatingElements, of which the following is a specification.

My invention relates to electrical heating elements.

I have discovered that alloys of iron and chromium have high specificresistance and are practically non-oxidizing and non-corrosive up toabout 1300 F. Higher temperatures can be used, but the properties ofthese alloys are not so desirable for electrical heat ing units attemperatures substantially higher than 1300 F.. say, from about1600-1800 F., particularly when run continuously for many hours at atime.

The quantity of chromium used depends on the uses to which the heatingelement is put.

For electrical heating elements to be run at comparatively lowtemperatures, the proportion of chromium may be low, say from about 4%upwards. For higher tem eratures, the proportion of chromium shou d begreater, and from about 12% of chromium and upward for'red heat elementsgives good results. At present relative costs, about 30% to 40% chromiumcontent is about the limit for economical production but. if desired,more chromium can be used, pract cally u to 95% or even 100% chromium,though it is to be understood that I do not claim the use of chromiumper se as an electrical heating element, but only chromium when al- Alsothe higher ChIOL lum material is more difiicultto work mechanically.

When iron-chromium alloys are worked inheated state, as by forging, forexample, there is a considerable production of oxides, scale and thelike. When electrically heated,

however, without working. these materials are substantially free fromoxidation and corrosion and, having substantially high specificresistance, are well adapted f r use as electrical heating elements. Thefact at they oxidize and scale when worked at high temperatures,together with the known susceptibility of iron itself to scaling andOK!- dizing at high temperatures,

been responsible for failure heretofore of has apparently investigatorsin this field to discover th adaptability of these alloys for use aselectrical heating elements.

The carbon content preferably does not exceed a maximum of about 1%which is permissible in alloys containing about 12% of chromium or over,though lower carbon, say from about .10%.60% is better in such material.Silicon up to about 45% in the material having 12% or more of chromiumand proportionately lower silicon in lower chromium material down toabout 20% or less in 49;- chromium material does not materially affectthe alloy when made use of as a heating element.

Other metals, such as nickel. molybdenum, tungsten. etc.. may be presentin small quantities up to about 2-47 without marked effect on thequalities of the heating elemeutj Small quantities of various lmpuritiessuch as phosphorus, copper, tin and'the like, may, of course. bepresent, but are preferably reduced to the minimum conformable witheconomical production of the material.

It will be seen that my new heating element containing as it does, alarge proportion of iron, is of low cost as compared with the expensivealloys heretofore used for this purpose. I find, for example, that aheating element such as described and containing only about 14% ofchromium and the principal part of the remainder iron has substantiallythe same qualities and usefulness as a heating element containing sev--.6% of carbon and the principal part of the v remainder iron.

In testimony that I claim the foregoing I hereto set my hand, this 29thday of April, 1919.

. PERCY A. E. ARMSTRONG.

